Compressed-gas circuit breaker having contacting interrupting and isolating contactswith sequential operation



July 25, 1967 w. A. FISH. JR 3,333,077

SSEDGAS CIRCUIT BREAKER HAVING CQNTACTING INTERRUPTING AND ISOLATINGCONTACTS COMPRE WITH SEQUENTIAL OPERATION 2 Sheets-$heet 1 Filed Nov.19, 1964 NF a EP mommumaioo cub zu- 024 W fr- ATTORNEY y 1967 w. A.FISH. JR 3,333,077

COMPRESSED-GAS CIRCUIT BREAKER HAVING CONTACTING INTERRUPTING ANDISOLATING CONTACTS WITH SEQUENTIAL OPERATION Flled Nov 19, 1964 2Sheets-Sheet 2 9 mfg United States Patent 3,333,077 COMPRESSED-GASCIRCUIT BREAKER HAVING CONTACTING IN TERRUPTING AND ISOLATING CONTACTSWITH SEQUENTIAL OPERATION William A. Fish, Jr., Wilkins Township,Pittsburgh, Pa.,

assignor to Westinghouse Electric Corporation, Pittsburgh, Pa., acorporation of Pennsylvania Filed Nov. 19, 1964, Ser. No. 412,354 12Claims. (Cl. 200-148) This invention relates, generally, to circuitbreakers and, more particularly, to circuit breakers of the gas-filleddual-pressure type in which a blast of high-pressure gas assists in arcinterruption during opening of contact members of the breaker.

Prior dual-pressure gas-filled circuit breakers have been operated by apneumatic operating mechanism located externally of the breaker andconnected to the contact members through a mechanical linkage. The flowof gas from the high-pressure chamber for are interruption has beencontrolled by a mechanically operated blast valve. A gasoperated controlsystem using the pressure differential between the high and low pressurechambers, thereby eliminating the need for a separate pneumaticoperating mechanism and compressed air system, is disclosed in acopending application, Ser. No. 419,044, filed Dec. 17, 1964 by G. J.Easley, and assigned to the Westinghouse Electric Corporation.

In order to secure fast interruption of a circuit, it is desirable toopen the contact members of a breaker and provide the contact separationrequired for most efficient arc interruption as quickly as possible.Accordingly, an object of this invention is to increase the speed ofopening of a gas-operated circuit breaker.

It is also desirable to provide additional contact separation afterinterruption has occurred to prevent flash-over due to surge voltages.However, increasing the contact separation beyond that required forefficient interruption before a current zero, and thus an opportunity tointerrupt occurs, can result in undesirably high are voltage and areenergy. Therefore, another object of the invention is to provide delayedadditional contact separation in a circuit breaker.

A further object of the invention is to provide a simplifiedgas-operated control scheme for a circuit breaker.

Still another object of the invention is to incorporate the blast valveof a circuit interrupter in the operating cylinder that withdraws theinterrupter contact.

A still further object of the invention is to utilize the hollow contactmember of an interrupter of the orifice type as part of an isolatorassembly, which is operated after arc interruption.

Another object of the invention is to utilize the isolator to disconnecta resistor which parallels the interruper contacts of the interni-pter.

Other objects of the invention will be explained fully hereinafter, orwill be apparent to those skilled in the art.

In accordance with one embodiment of the invention, two movableinterrupting and isolating contacts are combined into one pair ofcontact members which are operated in sequence by pistons in twocylinders pressurized by gas from the high-pressure reservoir of adual-pressure gas-filled circuit breaker. The sequence of operation issuch that the movable interrupter contact is withdrawn first, separatingthe contacts and permitting high-pressure gas from a blast tube to flowthrough the interrupter and the hollow section of the isolator pistonrod. At full travel of the movable interrupter contact, the interruptercontact and are horn provide the necessary separation for eflicientinterruption. After a short delay to permit completion of theinterruption, the movable isolator piston rod is withdrawn to increaseand maintain contact separa- 3,333,077 Patented July. 25, 1967 tion, andthe movable interrupter contact and are horn are returned to the initialor closed position, thus stopping the flow of gas. The operation of thetwo pistons is controlled by gas operated valves which, in turn, are controlled by electrically operated valves.

For a better understanding of the nature and objects of the invention,reference may be had to the following detailed description, taken inconjunction with the accompanying drawings, in which:

FIGURE 1 is a diagrammatic vieW of one pole unit of a circuit breakerand control system embodying principal features of the invention, thecontact structure being shown in the closed-circuit position;

FIG. .2 is a view, in section, of the interrupter, the interrupter, theinterrupter operating cylinder and the isolator utilized in the circuitbreaker, again the contact structure being shown in the closed-circuitposition; and,

FIG. 3 is a view, in section, of a modified interrupter and shuntingresistor which may be utilized in the circuit breaker, the contactstructure again being shown in the closed position.

Referring to the drawings, and particularly to FIG. 1, there is showntherein a diagrammatic view of one pole unit and the associated controlapparatus for a circuit breaker 1 embodying the present invention. Itwill be understood that additional pole units, similar to the one shown,may be provided. The structure shown in FIG. 1 comprises a generallycylindrical tank 2, a pair of terminal bushings 3 extending through awall of the tank 2, a movable interrupter contact operating means ormotor 4, an interrupter unit 5, an isolator device 6, a high pressuregas reservoir 7, a compressor and filter 8 and an auxiliary switchoperating cylinder 9. As shown, control valves A, B and C are mountedinside the tank 2. A close valve 11 and a trip valve 12 are mountedexternally ofthe tank 2.

The tank 2 contains an interrupting gas, such as sulfur hexafiuoride (SPgas, at a relatively low pressure, for example 40 p.s.i.g. The reservoir7 contains SP gas at a relatively high pressure, for example 230p.s.i.g. The gas in the reservoir 7 is maintained at the high pressureby the compressor 8, which is connected between the tank 2 and thereservoir 7 to form a closed system and returns gas from the tank 2 tothe reservoir 7 after an interrupting operation. The high-pressure gasreservoir .7 is

connected to the operating cylinder 4 through an insulating blast tube13.

The bushings 3 may be of any suitable construction, each bushing havinga supporting plate 14 attached to the lower end of a terminal stud 15which extends through the bushing. A current transformer 16 may bemounted around each bushing externally of the tank 2. The control valveA is a three-way, normally-closed, pressure-pilot-operated valve. Thevalve B is a three-way, normally-closed, pressure-pilot-operated valvewith an internal bleed between the pilot section and the outlet asindicated by the dotted line b. The valve C is a straightway,normally-closed, pressure-pilot-operated valve. The close valve 11 is astraight-way, solenoid-operated, normally-closed valve of adequatecapacity to pressurize the small pilot line 10 to valve B. The tripvalve 12 is a threeway, solenoid-operated, normally-closed valve of:adequate capacity to pressurize or to exhaust the small pilot lines 20,20a to valves A and C. One each of the close and the trip valves isrequired per breaker. One each of valves A, B and C is required perpole. i

As shown, a piston 17 is disposed inside the auxiliary switch operatingcylinder 9. Contact members 18 and 19 are carried by a piston rod 21attachedto the piston 17. The lower end of the cylinder 9 is connectedto the high pressure reservoir 7 through a line 22. The upper end of thecylinder 9 is connected to a port K' in the isolator cylinder 57 througha line 23. When hgih pressure gas is admitted to the upper end of thecylinder 9, the piston 17 is retained in its lowermost position, asshown in FIG. 1, in view of the difference in area of the two sides ofthe piston 17. When the high pressure gas is exhausted from the upperportion of the cylinder 9, the piston 17 is raised by the pressure ofthe high-pressure gas in line 22. The function and operation of theauxiliary switch 24, which is Operated by the piston 17, will bedescribed more fully hereinafter.

The movable interrupter contact operating means 4, is the interrupterunit 5 and the isolator operating device 6 are shown in more detail inFIG. 2. The movable interrupter contact operating means 4 comprises abase 25, a cylinder 26, a piston 27, a spring 28, a piston head 29 and avalve seal 31. As shown in FIG. 1, the base 25 is attached to thesupporting plate 14 on the right-hand terminal bushing 3. The cylinder26 is divided into two compartments 32 and 33 by a partition 34. Thecompartment 33 is closed by a cylinder head or cap 35 removably attachedto the right-hand end of the operating cylinder 26. The piston 27, whichis disposed in the compartment or entrance chamber 32, has an integrallyformed stem 36 which extends through the partition 34 into thecompartment 33. The piston head 29 is attached to the end of the stem 36by a nut 37. An O-ring seal 38 is provided around the stem 36 in thepartition 34. A similar seal 39 is provided at the joint between thecylinder head 35 and the cylinder 26. Likewise, a seal 41 is provided atthe joint between the cylinder 26 and the base 25. The piston 27 alsohas an integrally formed movable contact rod 42, which extends throughthe base 25 into an interrupting chamber 43 enclosed by an interrupterhood, or orifice member 44. The spring 28 surrounds the stem 36 in thecompartment 32 between the partition 34 and the piston 27. An opening 45through the base 25 connects the interrupting chamber 43 with the region47 between the lefthand side of the piston 27 and the valve seal 31.Small bleed holes 46 extend through the piston head 29.

A normal condition of the movable interrupter contact operating means 4is the closed contact position as shown in FIGS. 1 and 2. The frontcompartment, or chamber 32 formed by the cylinder 26, the partition 34,the piston 27 and the seal 31 is at high gas pressure, which ismaintained through the blast tube 13 from high-pressure gas reservoir 7.The regions 33a, 33b on both sides of the piston head 29 in thecompartment 33, and the region 47 between the piston 27 and the base 25are at low or tank pressure. Thus, the piston 27 is held closed againstthe valve seal 31 by the force of the high-pressure gas acting on theright-hand face of the piston 27 combined with the force of thecompression spring 28.

As shown, the interrupter unit 5 comprises the orifice member 44 and acluster of movable contact finger members 51 having a base 52, which isattached to the lefthand end of the piston rod 42 by means of an archorn 53. Contact fingers 54 are attached to the base 25 to slidablyengage the contact rod 42. The orifice member 44 is preferably composedof a suitable high-temperature material, such aspolytetrafluoroethylene. The orifice nember 44 is removably attached tothe base 25 by a :lamping ring 55.

The isolator operating device 6 comprises a base 56, a. cylinder 57, acylinder head or cap 58, and a piston 59. kn O-ring gasket 61 seals thejoint between the cylinder vall 57 and the cap 58. A seal 62 at theleft-hand end of he cylinder chamber 60 is engaged by the piston 59 whenhe piston is at the left-hand end of the cylinder chamber 50. The piston59 has an integrally formed isolator rod 53 which extends through thebase 56. An O-ring seal 64 s provided around the rod 63 at the openingthrough the use Contact fingers 65 are attached to the base 56 to:lidably engage the piston rod 63. As shown in FIG. 1, the iase 56 isattached to the supporting plate 14 on the leftland bushing 3.

As shown, the right-hand end of the isolator piston rod 63 has a hollowor tubular portion 66, which substanitally fills an opening 67 in theinterrupter orifice member 44 and is engaged by the contact fingers 51when the circuit breaker 1 is in the closed position. Interruptingopenings or vents 68 are provided in the wall of the tubular portion 66of the isolator contact member to accommodate exhausting of thearc-extinguishing gas.

The region or chamber between the right-hand side of the isolator piston59 and the base 56 is permanently connected to the blast tube 13 andhence to high pressure through a port L. Thus, the isolator is closed oropened by pressurizing or exhausting the region or chamber 60 formed bythe cylinder cap 58, the cylinder 57 and the left-hand side of thepiston 59.

The method of arc interruption is similar to that described in US.Patent 3,154,658, issued Oct. 27, 1964 to R. G. Colclaser and R. N.Yeckley and assigned to the Westinghouse Electric Corporation.High-pressure gas is blasted into the hollow contact member 66 and outthrough the vents 68 into the low pressure tank. The contact fingermembers 51 are sepaarted from the isolator contact member 66 by movingthe piston 27 to the right. When the piston 27 moves to the right, highpressure gas from the reservoir 7 flows through the blast tube 13 intothe compartment 32 of the cylinder 26 and out through the openings 45into the interrupting chamber 43 and thence into the hollow contactmember 66 to extinguish the established arc.

Thus, the hollow contact 66 is part of the isolator assembly 6 and theblast valve is incorporated in the operating means 4 that withdraws theinterrupter contact member 51 to the open position. The sequence ofoperation is such that the interrupter contact 51 is first withdrawn,separating the contact fingers 51 from the isolator cnotact member 66,and permitting high pressure gas from the blast tube 13 to flow throughthe interrupter unit 5 and the hollow section 66 of the movable isolatorcontact 63. At full travel, the interrupter contact 51 and are horn 53provide the necessary sepaartion for efiicient arc interruption. After ashort delay to permit completion of the interruption of the arc, themovable isolator contact 63 is withdrawn toward the left to increase andmaintain contact separation, and the piston 27 and the interruptercontact 51 return to their initial or closed position, thereby stoppingthe flow of high pressure gas.

The opening, or interrupting operation is initiated by admitting highpressure gas to port F. This pressurizes the chamber 33a in front of thepiston head 29 and drives the piston and the interrupter contact 51 tothe open position. This separates the contact members 51 and 66 (whichremains stationary) and opens the blast valve, permitting gas to flowthrough the interrupter orifice 44 and the hollow end of the movableisolator contact to interrupt the resulting are. The small bleed holes46 in the piston head 29 permit the pressure on the two sides of thepiston head to equalize and the interrupter contact 51 to return to theinitial or closed position under the action of the spring 28. The sizeof the bleed holes 46 will determine the length of time the interruptercontact 51 and blast valve 27 remain open, and will be selected topermit reclosure as soon as possible after allowing adequate time forinterruption of the arc to be completed. When port F is again reduced tothe low pressure, the chamber 33a will exhaust and the interrupteroperating piston 29 will remain in the normal closed position. A checkvalve 69 (FIG. 1) between ports F and G also quickly exhausts thechamber 33b behind the piston head 29 so that the opening operation canbe repeated quickly if desired.

As shown in the drawings, the breaker is in the closed circuit position.The close valve 11 and the trip valve 12 and the valves A and C aredeenergized and closed. The isolator chamber 60 is pressurized and thepilot 71 of valve B is maintained at high pressure by the internal bleedconnection b, thus holding this valve in the open position and admittinghigh pressure gas to maintain the pressurized condition of the isolatoroperating device 6. The low pressure condition in the compartment 33 ofthe interrupter operating cylinder 26 is maintained through the openexhaust port of the normally closed valve A.

Energizing the solenoid 72 of the trip valve 12 admits high pressurethrough the pilot line 20' to the pilot 73 of the valve A which opensand admits high pressure to the interrupter operating chamber 33athrough the port F. The interrupter contacts 51, 66 then separatepermitting gas flow through the interrupter unit and the contact 51recloses after a short delay as previously explained. The trip valve 12also admits high pressure through the pilot line 20a to the pilot 74 ofthe valve C, which opens and exhausts the pilot 71 of valve B to lowpressure. This permits valve B to close moving upwardly under theinfluence of spring 71', thus exhausting the isolator cylinder 60 to lowor tank pressure through exhaust opening 71". The piston 17 in theauxiliary switch operating cylinder 9 is operated by the pressure changeat port K of the isolator chamber 60, thus opening the contact members19 of the auxiliary switch 24 and deenergizing the solenoid 72 of thetrip valve 12. The trip valve 12 returns to its normally closedposition, exhausting the pilots of valves A and C which return to theirnormally closed positions. This exhausts the interrupter operatingchamber 33a and isolates the pilot 71 of the valve B except for theinternal bleed connection b which is connected to the isolator chamber60 (now at low tank pressure). The compression spring 71 of valve B willnow maintain the valve B in its upwar-d position (not shown) exhaustingthe isolator chamber 60 through exhaust opening 71".

The isolator region 60 thus remains exhausted through valve B to lowtank pressure, and the isolator contact 66 remains in its leftward fullyopen position. Since the interrupter operation is initiated bypressurizing a very small volume 33a between the one side of the pistonhead 29 and the partition 34 in the cylinder 26, and the isolatorcontact opening is initiated by exhausting a relatively large volume 60in the cylinder 57 between the piston 59 and the cylinder head 58, theinterrupter contact 51 will open sooner than the isolator contact 66.The desired time sequence and time intervals of interrupter open,isolator open and interrupter reclose can readily be obtained byselection of the proper size of gas passages.

Energizing the solenoid 75 of the close valve 11 admits high pressurethrough the pilot line 10 to the pilot 71 of valve B which opens, movingdownwardly and admits high pressure to the isolator chamber 60 throughpressure line 30, thus closing the isolator contact 66. The pressurechange at port K operates the auxiliary switch 24 to open its contactmembers 18 and hence deenergize the solenoid 75 of the close valve 11.The pilot 71 of valve B is maintained at high pressure by the internalbleed connection b to the now pressurized isolating chamber 60 and thebreaker stays closed.

The gas flow capacity of valve C should be greater than that of theclose valve 11 to assure pneumatically trip-free operation of theisolator contact 66. Any standard, non-pumping electrical control schemewhich provided seal-in on both closing and opening operations isapplicable to this circuit breaker although not shown in the drawings.

A well known principle in circuit interruption is that performance canbe improved and ratings can be increased by adding a shunt resistor inparallel to the main separating contacts while interrupting the mainfault current, and then opening the resistor circuit to interrupt theresidual resistor current. In the modification shown in FIG. 3, aresistor 76 is wound around the interrupter orifice member 44' and isconnected across the interrupter contact member 51 and the isolatorcontact member 66 by means of a spring-biased contact member or, probe77, which engages the isolator contact member 66 when it is in theclosed position, as shown in FIG. 3. As shown, contact member 77 isslidably disposed in an enlarged end portion 78 of the insulatingorifice member 44' and is biased into engagement with the isolatingcontact member 66 by a spring 79. Contact member 77 is connected to oneend of the resistor 76 by a connector 81. The other end of the resistor76 is connected to the base 25 by a connector 82. If desired, resistorsof other types, such as carbon block or disc resistors, may be utilizedin place of the wire resistor 76.

Interruption of the main fault current is accomplished, as hereinbeforedescribed, by the flow of high-pressure gas into the hollow isolatorcontact member 66 when the main interrupter contact member 51 and thearc horn 53 are withdrawn to the right. The resistor interrupter probe77 remains in contact with the isolator contact member 66, thus shuntingthe current through the resistor 76 when the arc has been extinguished.When the isolator piston rod 63 is withdrawn toward the left, the

residual current arc is drawn between the interrupter probe 77 and theisolator contact member 66, and is interrupted by the continued flow ofhigh-pressure gas out through the orifice opening 40. The movableisolator contact 66 continues its movement to the open position, thusmaintaining contact separation, and the main interrupter piston 27returns to the leftward closed position over the valve seat 31, thusstopping the flow of gas.

The closing operation of the modified-type interrupting unit 50 is thesame as hereinbefore described in connection with the interrupter ofFIG. 2. The isolator contact 63 is moved to the closed position andcontact is made by engaging first the resistor interrupter probe 77 andthen the main interrupter contact 51, thus completing the circuit.

From the foregoing description, it is apparent that the inventionprovides a circuit breaker in which fast contact separation required fortwo or three cycle interrupting time is readily obtainable. The physicaldisturbance on interruption of the arc is kept to a minimum bycompleting the interruption with an ideal contact separation distance,after which the separating distance is increased by the operation of theisolator device 6 to prevent flash-over due to surge voltages. The gasblast time is reduced to a minimum, thus reducing the amount of gasreservoir volume and the amount of time during which the compressor 8 isrequired to operate and maintain high pressure in the high pressurereservoir 7. The combining of the interrupter and isolator contacts andincorporating the blast valve in the interrupter operating cylinderreduces the number of parts and simplifies the breaker structure,thereby decreasing the cost, improving the reliability and reducingmaintenance requirements.

Since numerous changes may be made in the above described constructions,and diiferent embodiments of the invention may be made without departingfrom the spirit and scope thereof, it is intended that all subjectmatter contained in the foregoing description, or shown in theaccompanying drawings shall be interpreted as illustrative and not in alimiting sense.

I claim as my invention:

1. A circuit breaker of the compressed-gas type including, incombination, means defining an orifice member having an orifice openingtherein, a movable interrupting contact disposed within said orificemember, a movable isolating contact movable through said orifice openingduring the closing operation and into contacting closed engagement withsaid movable interrupting contact, means defining an entrance chamberfilled with high-pressure gas disposed on one side of said orificemember, said entrance chamber having a blast opening leading into saidorifice member, blast-valve means including a movable blast valveresponsive to movement of said movable interrupting contact forcontrolling a flow of high-pressure gas out of said entrance chamber andinto said orifice member, first operating means for causing an initialretraction of said movable interrupting contact away from said movableisolating contact within said orifice member while the movable isolatingcontact is stationary during the initial portion of the openingoperation, said retracting separating movement of the movableinterrupting contact effecting opening of said blast-valve means forcausing a blast of high-pressure gas to flow through said blast openingfrom the pressurized entrance chamber into said orifice member forarc-extinguishing purposes, and second operating means for subsequentlyeffecting isolating movement of said movable isolating contact out ofsaid orifice opening to interpose an isolating gap into the circuit.

2. The compressed-gas circuit breaker according to claim 1, wherein atank at relatively low pressure is provided, two terminal bushingsextend into said tank, the orifice member and first operating means aresupported at least partially by the inner end of one terminal bushing,and the movable isolating contact and second operating means is at leastpartially supported by the inner end of the other terminal bushing.

3. The compressed-gas circuit breaker according to claim 1, wherein thefirst operating means comprises a pneumatic operating cylinder and afirst piston member movable therein and secured to the movableinterrupting contact.

4. The combination of claim 3, wherein means are provided to bias themovable interrupting contact to the closed-circuit position.

5. The combination according to claim 1, wherein means are provided tobias the movable interrupting contact to the closed-circuit position.

6. The compressed-gas circuit breaker according to claim 1, wherein thesecond operating means comprises a pneumatic operating cylinder and asecond piston member movable therein and secured to the movableisolating contact.

7. The compressed-gas circuit interrupter according to claim 3, whereinthe second operating means comprises a pneumatic operating cylinder anda second piston member movable therein and secured to the movableisolating contact.

8. The combination according to claim 2, wherein a high-pressure blasttube extends from the tank wall to the entrance region at high pressureto maintain the same pressurized at high pressure.

9. The combination according to claim 3, wherein the region (33b) withinthe operating cylinder on one side of the first piston member isgenerally at low pressure, the region (33a) within the operatingcylinder on the other side of the first piston member is alternatelypressurized and exhausted, and conduit means and unidirectional valvemeans (69) interconnect the two regions for rapid reopening operations.

10. The combination according to claim 1 wherein a resistance contactmember (77) is supported in the orifice member and bears against themovable isolating contact, and a resistance is connected between saidresistance contact member (77) and the movable interrupting contact.

11. A circuit breaker comprising a tank containing an interrupting gasat a relatively low pressure, a reservoir containing the same kind ofgas at a relatively high pressure, an interrupting chamber disposedinside the tank, a movable interrupting contact member and a movableisolating contact member engaging within the chamber, a first pistondisposed in a first cylinder for withdrawing the movable interruptingcontact member, a second piston disposed in a second cylinder forwithdrawing the movable isolating contact member, valve means forcontrolling the admission of gas into said cylinders from the highpressure reservoir first to withdraw the interrupting contact member inone direction and then to withdraw the isolating contact member in theopposite direction, auxiliary switch means for controlling the operationof containing the same kind of gas at a relatively high pressure in saidsecond cylinder for operating the auxiliary switch means.

12. A circuit breaker comprising a tank containing an interrupting gasat a relatively low pressure, a reservoir containing the same kind ofgas at a relatively high pressure, an interrupting orifice memberdisposed inside the tank, an interrupting contact member and anisolating contact member engaging within the orifice member, a firstpiston disposed in a first cylinder for withdrawing the interruptingcontact member, a second piston disposed in a second cylinder forwithdrawing the isolating contact member, valve means for controllingthe admission of gas into said cylinders from the high pressurereservoir to operate said pistons in sequential relation, and resistancemeans including a resistance contact supported in said orifice memberconnected in parallel circuit relation with said contact members.

References Cited UNITED STATES PATENTS 2,447,656 8/1948 Ludwig et al200-148 X 3,164,705 1/1965 Cromer 200148 FOREIGN PATENTS 512,623 9/1939Great Britain. 546,399 7/1942 Great Britain.

267,793 7/ 1950 Switzerland.

ROBERT K. SCI-IAEFER, Primary Examiner. R. S. MACON, Assistant Examiner.

1. A CIRCUIT BREAKER OF THE COMPRESSED-GAS TYPE INCLUDING, INCOMBINATION, MEANS DEFINING AN ORIFICE MEMBER HAVING AN ORIFICE OPENINGTHEREIN, A MOVABLE INTERRUPTING CONTACT DISPOSED WITHIN SAID ORIFICEMEMBER, A MOVABLE ISOLATING CONTACT MOVABLE THROUGH SAID ORIFICE OPENINGDURING THE CLOSING OPERATION AND INTO CONTACTING CLOSED ENGAGEMENT WITHSAID MOVABLE INTERRUPTING CONTACT, MEANS DEFINING AN ENTRANCE CHAMBERFILLD WITH HIGH-PRESSURE GAS DISPOSED ON ONE SIDE OF SAID ORIFICEMEMBER, SAID ENTRANCE CHAMBER HAVING A BLAST OPENING LEADING INTO SAIDORIFICE MEMBER, BLAST-VALVE MEANS INCLUDING A MOVABLE BLAST VALVERESPONSIVE TO MOVEMENT OF SAID MOVABLE INTERRUPTING CONTACT FORCONTROLLING A FLOW OF HIGH-PRESSURE GAS OUT OF SAID ENTRANCE CHAMBER ANDINTO SAID ORIFICE MEMBER, FIRST OPERATING MEANS FOR CAUSING AN INITIALRETRACTION OF SAID MOVABLE INTERRUPTING CONTACT AWAY FROM SAID MOVABLEISOLATING CONTACT WITHIN SAID ORIFICE MEMBER WHILE THE MOVABLE ISOLATINGCONTACT IS STATIONARY DURING THE INITIAL PORTION OF THE OPENINGOPERATION, SAID RETRACTING SEPARATING MOVEMENT OF THE MOVABLEINTERRUPTING CONTACT EFFECTING OPENING OF SAID BLAST-VALVE MEANS FORCAUSING A BLAST OF HIGH-PRESSURE GAS TO FLOW THROUGH SAID BLAST OPENINGFROM THE PRESSURIZED ENTRANCE CHAMBER INTO SAID ORIFICE MEMBER FORARC-EXTINGUISHING PURPOSES, AND SECOND OPERATING MEANS FOR SUBSEQUENTLYEFFECTING ISOLATING MOVEMENT OF SAID MOVABLE ISOLATING CONTACT OUT OFSAID ORIFICE OPENING TO INTERPOSE AN ISOLATING GAP INTO THE CIRCUIT.